Cruise Control System Buick Roadmaster VIII

DESCRIPTION & OPERATION

BODY CODE IDENTIFICATION

BODY CODE IDENTIFICATION

Cruise control system uses a control module to obtain desired vehicle cruise operation. An electronic controller and an electric stepper motor are 2 important components in the cruise control module. Controller monitors vehicle speed and operates electric stepper motor. Stepper motor moves throttle linkage.

Cruise control module contains a low speed limit to prevent cruise engagement below a minimum speed of 25 MPH. System capabilities include cruise, coast, resume speed, accelerate, "tap-up" and "tap-down". Control switches located on multifunction turn signal lever operate controller. Electric brake switches mounted on brake pedal bracket disengage cruise system when brake pedal is depressed.

ENGAGEMENT SWITCH

The engagement switch turns cruise control system on and off. With switch pushed to ON position and SET button pushed in, cruise speed should be maintained. With cruise in RESUME/ACCELERATE (R/A) position, cruise speed can be resumed after slowing down or stopping.

With cruise in R/A position, cruise speed can be raised (tap-up) or lowered (tap-down) in one MPH increments. Cruise control engagement switch is located in multifunction lever, which serves as turn signal lever and wiper switch.

CRUISE CONTROL MODULE

Cruise control module is mounted on left side of engine compartment near master cylinder. Cruise control module has an electronic controller and an electric stepper motor to vary throttle with each cruise control mode.

BRAKE & CLUTCH RELEASE SWITCHES

On automatic transmission models, a brakelight/Torque Converter Clutch (TCC) switch and a cruise control release switch mounted on brake pedal bracket are used to disengage cruise system electrically when brake pedal is depressed. Manual transmission models also use a clutch start switch and cruise control clutch anticipate switch (3.4L) or cruise control release switch (5.7L) to stop cruise operation. (Scheme 1)or (Scheme 2). Speed of vehicle at brake actuation will be stored in cruise control module memory.

Scheme 1

Scheme 2

VEHICLE SPEED SENSOR (VSS)

A Permanent Magnet (PM) generator, driven by transmission, generates an output frequency of vehicle speed information. This frequency is sent to VSS buffer ("B" body) and to ECM, where signal is amplified and sent to cruise control module for cruise control operation.

"B" Body

VSS buffer receives a signal from VSS indicating speed of vehicle. This signal is processed by VSS buffer and supplied to ECM, cruise control module and speedometer. VSS buffer is located on convenience center left of steering column.

BRAKE & CLUTCH RELEASE SWITCHES ADJUSTMENT

Depress brake pedal and insert brakelight/TCC and cruise control release switches into proper switch receptacles until fully seated. Slowly pull brake pedal back to its fully retracted position (requires 50 lbs. of force). TCC/cruise control and brakelight switch will move within switch retainers to proper adjustment.

Remove air cleaner and resonator. Unlock cable conduit at accelerator cable bracket, cable adjuster spring will take up slack. (Scheme 3) Ensure throttle plate is fully closed. Lock cable conduit at accelerator cable bracket by pressing down on lock tab. Reinstall air cleaner and resonator.

"F" Body

Information not available from manufacturer.

Scheme 3

Preliminary Checks

1. To resolve any cruise control system malfunction, perform a visual inspection of all components. Check system to ensure there are no blown fuses, damaged or disconnected electrical wires or poor connections. Check high mounted brakelight bulbs; if burned out, cruise control system will not function.
2. With ignition switch in RUN position, battery voltage is applied to terminal "F" of cruise control module. (Scheme 4) When cruise control switch slider is moved to ON position, battery voltage is applied to terminal "A" of module connector.
3. When brake pedal is released, battery voltage should be present at module terminal "D". When brake pedal is depressed, battery voltage should be present at module terminal "G". When cruise switch slider is moved to R/A position, battery voltage should be present at terminal "C" of module connector.
4. With SET button depressed, battery voltage should be present at module terminal "B". With vehicle moving faster than 25 MPH, voltage at module terminal "K" will oscillate from 0-5 volts. Module ground is at terminal "E".

Scheme 4

CRUISE CONTROL WILL NOT ENGAGE, SPEEDOMETER INOPERATIVE

Check vehicle speed sensor. See VEHICLE SPEED SENSOR (VSS) under TESTING . Check for ECM trouble Code 24. See appropriate G - TEST W/CODES article in the ENGINE PERFORMANCE Section.

CRUISE CONTROL WILL NOT ENGAGE, SPEEDOMETER OPERATES NORMALLY

1. Turn ignition off. Disconnect cruise control module connector. Turn ignition switch to RUN. Using a test light, check for battery voltage at terminal "F" of cruise control module harness connector. If battery voltage is present at terminal "F", go to next step. If battery voltage is not present at terminal "F", check fuses and check wire to terminal "F" for open or poor connection. See WIRING DIAGRAM.
2. Using a DVOM or test light, check module ground at terminal "E". If module ground is okay, go to next step. If module ground is not okay, service Black or Black/White wire from chassis ground to cruise control module. 3) Ensure ignition switch is still in RUN position. Set cruise control slider switch to ON position. Using a test light, check for battery voltage at terminals "B" and "C" of cruise control module connector. If battery voltage is not present at either terminal "B" or "C", go to next step. If voltage is present at terminal "B", check Dark Blue wire for short to battery voltage. If voltage is present at terminal "C", check Dark Green wire (Gray/Black wire on "F" body) for short to battery voltage.
3. Using a test light, check for battery voltage at terminal "A" of cruise control module connector. If battery voltage is present, go to step 6). If battery voltage is not present at terminal "A", check for battery voltage to cruise switch. (Check at connector at base of steering column). Battery voltage should be present at Dark Blue wire (Pink wire on "F" body). If battery voltage is present, go to next step. If battery voltage is not present, check for open in Dark Blue wire (Pink on "F" body) between fuse panel and cruise control switch.
4. Check for open in Gray wire between cruise control switch and cruise control module. Repair Gray wire if necessary. If Gray wire is okay, replace cruise control switch/multifunction lever assembly.
5. Check for battery voltage at terminal "D" of cruise control module connector. If battery voltage is present, go to next step. If battery voltage is not present, backprobe Pink wire (Dark Blue on "B" body) at clutch pedal switch (M/T) or brake pedal switch (A/T). If battery voltage is not present, service Pink wire (Dark Blue on "B" body) as necessary. If voltage is present, check clutch or brake pedal switch operation, replace as necessary.
6. Check brakelight operation. If okay, go to next step. If brakelights do not operate properly, backprobe Orange wire of brakelight switch connector. If voltage is not present, service Orange wire to STOP/HAZARD fuse in instrument panel fuse panel. If voltage is present at Orange wire of brakelight switch connector, backprobe Yellow wire of brakelight switch connector and press brake pedal. If battery voltage is not present, replace brakelight switch. If battery voltage is present, unplug brakelight switch connector. Using a DVOM, check for open in yellow wire between brakelight switch and cruise control module.
7. Connect a test light to terminal "B" of cruise control module connector. Press and hold SET switch. If test light glows, go to next step. If test light does not glow, check Dark Blue wire between cruise control switch and cruise control module for open. Repair Dark Blue wire as necessary. If Dark Blue wire is okay, replace cruise control switch/multifunction lever assembly.
8. If all above tests result okay, check function of VSS. See VEHICLE SPEED SENSOR (VSS) under «TESTING»(/buick/roadmaster/viii-1991-1996/remont/cruise-control-systems/#cruise-control-system) .

CRUISE CONTROL WILL NOT RESUME, ACCELERATE, TAP-UP OR TAP -DOWN

1. Turn ignition switch to RUN position. Set cruise control switch to ON position. Backprobe Dark Green wire (Gray/Black wire on "F" body) of cruise control switch. If test light does not glow, replace cruise control switch/multifunction lever. If test light glows, go to next step.
2. Check Dark Green wire (Gray/Black wire on "F" body) for open, repair wire as necessary. If Dark Green wire (Gray/Black wire on "F" body) is okay, check associated connectors for good connection. If okay, replace cruise control module.

1. If speedometer is inoperative, turn ignition on. Using a DVOM or test light, measure voltage at Pink/Black wire of VSS module connector. Battery voltage should be present.
2. If zero volts are present, check ECM fuse, check for open in Pink/Black wire from ECM fuse. If battery voltage is present, check VSS ground circuit.
3. Unplug connector at VSS. Using Signal Generator/Instrument Panel Tester (J-33431-B) and Adapter (J-33431-4), backprobe VSS connector terminal "A" (Purple wire) with positive probe and negative lead to ground.
4. Turn tester on and set to 54 MPH (60 Hz). Speedometer should read approximately 54 MPH. If speedometer does not read 54 MPH, check for short to ground, short to voltage in Purple wire, or poor connection at VSS or module. If wiring or connectors are okay, replace VSS module.
5. If speedometer reads 54 MPH, remove tester negative lead from ground and backprobe VSS connector terminal "B" (Yellow) wire. Speedometer should read approximately 54 MPH.
6. If speedometer does not read 54 MPH, check for short to voltage or open in Yellow wire. Ensure all VSS connections are tight. If wire and connectors are okay, replace VSS module. If speedometer reads 54 MPH, check for poor connections at VSS. If connectors are okay, replace VSS.
7. If trouble Code 24 is set, go to step 1). If Code 24 is not set, disconnect VSS module Black 3-pin connector. Using tester, connect positive lead to VSS module terminal "C" (Brown wire) and negative lead to ground.
8. Turn tester on and set to 54 MPH (60 Hz). Speedometer should read approximately 54 MPH. If speedometer reads 54 MPH, check for poor connection at VSS module terminal "C" (Brown wire). If connector is okay, replace VSS module.
9. If speedometer does not read 54 MPH, check Brown wire for short to voltage, short to ground or open. Ensure instrument cluster connector terminal No. 28 (Brown wire) is okay. If wire and connectors are okay, service instrument cluster.

1. Disconnect ECM connector containing Dark Green/White wire. Connect Red wire of Signal Generator Instrument Panel Tester (J-33431-B) to Dark Green/White wire. Connect Black wire of tester to a good ground. Set tester to 54 MPH. Turn ignition switch to RUN position.
2. If speedometer reads 54 MPH, check for poor connection at Dark Green/White wire of ECM connector. If okay, replace ECM. If speedometer does not read 54 MPH, check for open or short in Dark Green/White wire between ECM and Cruise control module and instrument cluster. Check for poor connection at instrument panel connector. If okay, service instrument cluster.

REMOVAL & INSTALLATION

1. Disconnect negative battery cable. Raise vehicle. Disconnect speed sensor electrical connector. Remove speed sensor retainer bolt, retainer and spacer. Remove speed sensor. Remove speed sensor "O" ring and gear from speed sensor.
2. To install, reverse removal procedure. Tighten speed sensor retainer bolt to 89 INCH lbs. (10.1 N.m).

Removal & Installation ("B" Body)

1. Disconnect VSS buffer harness connector from VSS buffer. Remove 2 convenience center retaining screws. Remove convenience center from cowl. Gently pry retainers and remove VSS buffer.
2. To install, reverse removal procedure. Tighten convenience center retaining screws to 88 INCH lbs. (9.9 N.m).

Removal

1. Remove air cleaner and resonator. Disconnect cruise control cable and clip from throttle body lever stud. Unlock cable conduit at accelerator cable bracket. Remove cable and conduit from accelerator cable bracket.
2. Remove cable from cruise control module. Compress conduit tangs and pull conduit out of cruise control stepper motor ribbon end fitting on module housing. Disconnect cable bead from cruise control motor ribbon end fitting on module. Note routing of cable from vehicle.

Installation

To install, reverse removal procedure. Adjust cruise control cable (if necessary). See CRUISE CONTROL CABLE ADJUSTMENT under ADJUSTMENTS.

1. Disconnect negative battery cable. Remove electrical connectors from switches. Remove switches from retainer. Remove retainer from brake pedal mounting bracket.
2. To install, reverse removal procedure. Adjust brake release switch. See «BRAKE & CLUTCH RELEASE SWITCHES ADJUSTMENT»(/buick/roadmaster/viii-1991-1996/remont/cruise-control-systems/#cruise-control-system__brake-clutch-release-switches-adjustment) under ADJUSTMENTS.

1. Disconnect negative battery cable. Disconnect cruise control module electrical connector. Disconnect cruise control cable from module. Remove cruise control module mounting screws. Remove cruise control module and grommet nuts. Remove grommet nuts from cruise control module if new module is used.
2. To install, reverse removal procedure. Tighten cruise control module mounting screws to 18 ft. lbs. (24 N.m).

CRUISE CONTROL SWITCH

Note. Cruise control switch is serviced by replacing entire multifunction lever.

Disconnect negative battery cable. Remove steering column housing cover end cap by pulling toward front of vehicle. Disconnect electrical connector. Ensure all switches and controls are in OFF position. Pull multifunction lever straight out (toward driver door). Remove multifunction lever. To install, reverse removal procedure.

See also:
• TESTING
• BRAKE & CLUTCH RELEASE SWITCHES ADJUSTMENT